A method comprises printing an image using a printhead cartridge including a number of dies, each die comprising a nozzle array, the printing comprising: determining a drop parameter of fluid drops ejected from nozzles of the nozzle array of at least one die; comparing the drop parameter to a threshold value; and determining an image characteristic of an image to be printed; and if the image characteristic meets a defined criterion and if the drop parameter exceeds the threshold value, applying a second print mask for printing the image; and if the image characteristic does not meet the defined criterion or if the drop parameter does not exceed the threshold value, applying a first print mask for printing the image, wherein the second print mask uses less nozzles of the nozzle arrays than the first print mask.
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1. A method for printing an image using a printhead including a number of dies, each die comprising nozzles to eject fluid drops onto a print medium, the method comprising:
determining a drop parameter, including a drop velocity, of the fluid drops ejected from the dies;
comparing the drop velocity of the fluid drops to a threshold value;
determining whether an image characteristic of the image to be printed meets a predefined criterion;
in response to a determination that the image characteristic of the image does not meet the predefined criterion or the drop velocity of the fluid drops does not exceed the threshold value, applying a first print mask for printing the image, wherein the first print mask uses all of the dies of the printhead to print the image; and
in response to a determination that both the image characteristic of the image meets the predefined criterion and the drop velocity of the fluid drops exceeds the threshold value, applying a second print mask for printing the image, wherein the second print mask disables at least one die of the printhead from being used to print the image.
13. A non-transitory computer-readable storage medium storing instructions that, when executed by a processor, cause the processor to:
control a printing apparatus to print an image by controlling a number of dies in a printhead cartridge of the printing apparatus to eject fluid drops onto a print medium;
determine a drop velocity of the fluid drops ejected from the dies;
compare the drop velocity of the fluid drops to a threshold value;
determine whether an image characteristic of the image to be printed meets a predefined criterion;
in response to a determination that the drop velocity of the fluid drops does not exceed the threshold value or the image characteristic of the image does not meet the predefined criterion, apply a first print mask for printing the image, wherein the first print mask uses all of the dies of the printhead cartridge to print the image; and
in response to a determination that both the image characteristic of the image meets the predefined criterion and the drop velocity of the fluid drops exceeds the threshold value, apply a second print mask for printing the image, wherein the second print mask disables at least one die of the printhead cartridge from being used to print the image.
9. A printing apparatus including:
a printhead cartridge having a number of dies, each die including nozzles to eject fluid drops to print an image on a print medium;
a drop detector to determine a drop parameter including a drop velocity of the fluid drops ejected from the nozzles of the dies; and
a controller to:
control firing of the nozzles of the dies to eject the fluid drops,
compare the drop velocity of the fluid drops to a threshold value,
determine whether an image characteristic of the image to be printed meets a predefined criterion,
in response to a determination that the image characteristic of the image does not meet the predefined criterion or the drop velocity of the fluid drops does not exceed the threshold value, apply a first print mask for printing the image, wherein the first print mask uses all of the dies of the printhead cartridge to print the image, and
in response to a determination that both the image characteristic of the image meets the predefined criterion and the drop velocity of the fluid drops exceeds the threshold value, apply a second print mask for printing the image, wherein the second print mask disables at least one die of the printhead cartridge from being used to print the image.
2. The method of
3. The method of
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10. The printing apparatus of
11. The printing apparatus of
12. The printing apparatus of
14. The non-transitory computer-readable storage medium of
measure a drop weight of the fluid drops ejected from each die;
determine an average drop weight of the measured drop weights;
determine the threshold value as a minimum deviation from the average drop weight; and
apply the second print mask if the drop weight of the fluid drops ejected from a minimum number of nozzles of one die exceeds the threshold value.
15. The non-transitory computer-readable storage medium of
analyze, based on print data, the image to be printed to detect a continuous area of the image to be printed by a solid color;
determine whether the continuous area covers a defined minimum area size; and
in response to a determination that the continuous area covers the defined minimum area size, determine that the predefined criterion is met.
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The present application is a national stage filing under 35 U.S.C 371 of PCT application number PCT/US2018/028847, having an international filing date of Apr. 23, 2018, the disclosure of which is hereby incorporated by reference in its entirety.
A color printer may include a number of printhead cartridges. A printhead cartridge may contain one or several printing fluids, wherein some of the printing fluids may be non-marking printing fluids, e.g., overcoats and the like and some printing fluids may be dies associated with a same color or with different colors. A die may provide a line or row of nozzles, also referred to as nozzle array or nozzle trench. When printing with a number of printhead cartridges, using a multiple-pass printing mode, masks may be applied to the nozzles to selectively deposit droplets of printing fluid on a print medium, pass by pass, to control the printing process. Print masks may help to prevent or reduce visible artifacts, such as image banding.
Examples are described with reference to the drawings.
Whereas, in the present application, a number of examples are described for illustration, this disclosure is not limited to these specific examples described and can be applied to similar devices, systems, methods and processes. The examples provided herein may be implemented in a large format printer, a desktop printer or another printing apparatus for dispensing printing fluid, such as ink. In one example the printing apparatus is an inkjet printer. Printhead cartridges may be provided on a carriage for scanning over a print medium in a print zone or printheads may be provided in form of a page-wide printing array. In some examples, a printhead cartridge contains one or several dies wherein each die is provided for a same color or for different colors. For example, one printhead may comprise between one and ten dies, each die having a nozzle array providing one or two or more rows of inkjet nozzles.
The printer further comprises a controller 22 (not shown in
Whereas this is not illustrated in detail, the printhead cartridges 16 may be replaceable and/or refillable cartridges. Additional ink supply cartridges may be provided within or externally to the printing apparatus and may be connected to the printhead cartridges via an ink tube assembly. The printer may comprise further components, such as a frame and supporting structure, a print medium feed system, motors, etc., which are not shown or described in detail.
Printhead assemblies can be different from the one shown in
There are different approaches for dealing with banding effects, such as applying masks to the nozzle trenches, the mask applying different ink usage per nozzle in an interleaving, weaving, pass programming selection, or other manner. In a multi-pass print mode, a mask is applied to the printhead cartridges during each pass so that a section or band of an image is composed by a number of pixels printed during the number of passes. In a three-pass print mode, for example, the print medium is advanced by one third of a swath height after each pass and the printhead cartridges are masked to print part of the image during each pass.
Ramped masks can be used, including an up-ramp, a flat middle part and a down-ramp, as illustrated in
Whereas the present disclosure is explained with reference to a mask applied to one printhead array comprised of two printhead cartridges dispensing a single color ink, the process as described herein can be adapted to masking printhead arrays of all colors and ink types, such as printhead arrays of C, M, Y, and K inks. The masking process can be applied irrespective of whether a printhead array is concentrated in one or a plurality of printhead cartridges dispensing a single color ink, as in the example of
In each of these masking schemes addressed above, more ink will be deposited by the middle section of the printhead array than by the edge sections, wherein the edge sections may comprise the entire outer edge dies or a part of the nozzles of the outer edge dies so that there is uneven usage of the printhead dies over the lifetime of a printhead cartridge.
Accordingly, due to the size and shape of print masks, e.g. having ramps in areas of overlap, nozzle in overlap and edge areas may be used less frequently than nozzle in center areas so that nozzle degradation is non-uniform. More frequently used nozzles may generate fluid drops of reduced drop velocity (DV) and/or reduced drop weight (DW). Uneven DV and DW may create image quality (IQ) defects wherein defects due to DW variation may be more visible in images with large areas of solid colors and defects due to DV variation may be more visible in images with vertical lines.
One way to address this phenomenon may be to determine a drop parameter of fluid drops ejected from the nozzles of the nozzle array of at least one die, comparing the drop parameter to a threshold value, and determining an image characteristic of an image to be printed. If the image characteristic meets a defined criterion and if the drop parameter exceeds the threshold value, a second print mask may be used for printing the image; and if the image characteristic does not meet the defined criterion or if the drop parameter does not exceed the threshold value, a first print mask may be used for printing the image. In other words, the second print mask is used when both conditions are met, the first print mask is used when one or none of the conditions is met. The second print mask may use less nozzles of the nozzle arrays than the first print mask.
This allows adjusting or selecting a print mask which disables non-uniformly operating nozzles, as a function of the image composition. In one example, nozzles may be disabled which generate a DW or DV which differs from an average DW or average DV by more than a threshold value. These nozzles may be disabled for images having a defined image composition, such as a large area of solid color or vertical lines, and may be enabled for other types of image compositions. Accordingly, the masking scheme may depend on both the state of the nozzles and the type of image to be printed. This reduces IQ defects and maintains throughput because print masks disabling some of the nozzles are used if useful for a particular image composition and are not used in other cases.
Similar curves could be established based on drop weight, for example. Drop velocity and drop weight may be detected by drop detector 20 and evaluated by controller 22.
Accordingly, if a variation of the drop parameter, such as drop velocity or drop weight, is detected which is above (or below) a certain threshold, such as above (or below) an absolute or relative value, the controller 22 may make a decision to modify or select a print mask 54 which disables some or all of the nozzles or dies which exhibit the variation, depending on the characteristics of the image to be printed. The threshold may be a relative parameter value calculated based on a defined percentage of an average value or of an initial value or of a nominal value of the drop parameter. Depending on how the threshold is defined, a threshold may be considered to be exceeded if the drop parameter is above or below the threshold. In the present examples described, the threshold is exceeded if the drop weight or drop velocity is above a respective drop weight threshold or drop velocity threshold.
In the example of
A modified mask will be applied if the drop parameter exceeds the threshold value and if the image characteristic meets a defined criterion, i.e. if both conditions are met. The image characteristic may be the presence of a continuous area of an image which is to be covered by a solid color, wherein the continuous area is at least 2%, at least 5% or at least 10% of the entire image area, for example. The image characteristic also may be a continuous area of the image which is to be covered by a solid color, wherein the continuous area is at least 1 cm2 or at least 4 cm2, for example. If the image characteristic is a continuous area of the image to be covered by a solid color, whether or not the image characteristic meets the defined criterion also may depend on the total size of the image. The solid color may be a single color or may include colors having a maximum color difference from a single color, the color difference being smaller than a given tolerance threshold. For example, the color difference may be determined according to a perceptually uniform color measure, such as a Euclidean distance in the CIELAB color space.
The above process of analyzing a drop parameter and determining an image characteristic and of adapting or selecting a mask as a function of drop parameter and image characteristic, can be performed separately for each printhead array associated with a respective different color, such as Cyan, Magenta, Yellow, and Black printhead arrays. A printhead array of a respective color may be formed from one or several printhead cartridges including single-color and multi-color cartridges and respective printhead dies.
The image characteristic additionally or alternatively may be the presence of vertical lines in an image, i.e. lines extending in the media advance direction. The image characteristic also could take into account a particular image pattern, such as a checkerboard pattern or another repetitive pattern, for example.
At 62, the information obtained from the drop detector is analyzed to calculate a drop parameter, such as drop weight and/or drop velocity. The drop parameter, such as drop weight and/or drop velocity, may be obtained for all nozzles of all dies of all printhead cartridges or for a portion thereof. The drop parameter may be visualized as a curve, as illustrated in
At 64, the calculated drop parameter is analyzed further, such as compared to a threshold, to determine whether the drop parameter of some or all of the nozzles of some of the dies exceed a threshold. The threshold may be a relative value, calculated based on an average value or median of the drop parameter, for example. A variation of the drop parameter of some of the nozzles or some of the dies above or below the threshold may indicate that there is uneven nozzle degradation which may result in noticeable image quality defects. If the drop parameter for some or all of the nozzles of some of the dies, e.g. for all or some nozzles of an edge die, exceeds the threshold, a process is triggered to determine whether an adaptive mask should be used. Additionally, if the drop parameter is the drop velocity and if it is determined that the drop velocity of some or all of the nozzles of some of the dies, e.g. of some or all nozzles of an edge die, exceeds the threshold, an alignment process may be triggered to compensate for the DV variation.
At 66, before printing, an image content of an image to be printed is analyzed to determine whether the image includes an image characteristic which meets a defined criterion, such as a minimum area of solid color. The image characteristic is one which may result in a noticeable image quality defect, such as banding, if the image was printed using the entire array of nozzles and dies exhibiting an uneven nozzle degradation. As explained above, after an extended lifetime, the nozzles located in the middle of a printhead array of one or several printhead cartridges may have been used more frequently than nozzle at the edges of the printhead array so that the nozzles at the edges of the printhead array may show less degradation than the majority of the nozzles in the middle. Accordingly, the nozzles at the edges of the printhead array will be able to eject fluid drops having a higher drop weight and/or higher drop velocity. To avoid noticeable image quality defects, the image content is analyzed to determine whether the image is such that the uneven nozzle degradation will be noticeable in the printed image. If this is not the case, a default mask, such as mask 52, may be used for printing.
At 66, an image having extended areas of solid colors is illustrated wherein this type of image may trigger adapting a mask or selecting a second mask 54 which disables some of the nozzles or dies determined to have a variation of the drop parameter above the threshold. The nozzles or dies determined to have a variation of the drop parameter above the threshold may be located at the outer edges of the printhead array. Accordingly, at 68, and adapted mask or second mask 54 can be selected for printing the image shown at 66, disabling the nozzles or dies at the outer edges of the printhead array.
At 72, it is determined whether the drop parameter exceeds a threshold, indicating that the associated nozzle exhibits a firing characteristic different from other nozzles, such as higher drop weight or higher drop velocity, as explained above. If yes, an image characteristic is determined at 74 wherein the image characteristic may relate to an area of solid color, for example. At 76, it is determined whether the image characteristic meets a defined criterion, such as an area of solid color greater than a defined size. If this criterion is met, the method proceeds with selecting a second mask, at 78. A second mask may be one which disables those nozzles which exhibit the firing characteristic different from other nozzles.
The sequence may be different from the one shown in
If, at 72, it is determined that the drop parameter does not exceed the threshold and/or if, at 76, it is determined that the image characteristic does not meet the criterion, the method proceeds to selecting a first or default mask, at 80. The first mask or default mask may be one which enables all nozzles, irrespective of whether they exhibit firing characteristic different from other nozzles
At 82, the selected first mask or second mask is used for printing.
Qian, Li, Castro Soriano, Javier, Recasens Oros, Ruben
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